1. Field of the Invention
The present invention relates to a failure detection method to detect an abnormal fabrication apparatus, which is used to manufacture semiconductor LSI circuits, based on the failure distribution for each wafer.
2. Description of the Related Art
To improve the manufacturing productivity of semiconductor LSI circuits, efforts for improvement in semiconductor LSI circuit yield continue to be made. To improve the yield, analysis of failures resulting in a decrease in the yield, identification of a manufacturing process, a fabrication apparatus, or LSI design rules causing failures have been made. However, LSIs are manufactured using several hundreds of fabrication processes, which are executed by several hundreds of fabrication apparatus. Therefore, it is difficult to identify a fabrication process and a fabrication apparatus resulting in failures, even if the failures in LSIs are identified.
There are roughly two types of LSI tests: a wafer test that is carried out before the fabrication process after the wafer manufacturing process, and a final test that is carried out after that fabrication process. The wafer test aims to decrease the number of failed chips entering the fabrication process. The final test aims to determine that LSIs satisfy performance requirements guaranteed by a manufacturer before shipment to users. In particular, the wafer test is carried out for circular wafers. By mapping and displaying failures in each wafer identified by the tests, the positions of those failures in that wafer can be determined. A fail bit map (FBM) for each memory device is a typical way to map failures.
The mapped wafer failures are roughly categorized according to two categories based upon the wafer failure distribution. The first category is for random failures, which evenly distributed within the wafer regardless of the positions therewithin; and the second category is for clustering failures, which are distributed unevenly. The clustering failures are considered to emanate from a certain fabrication process or a fabrication apparatus and cause a decrease in yield. The clustering failures are digitized, and the digitized values are then subjected to an inter-fabrication apparatus significant test.